Carbohydrates

Question 1

What are polymers?

Answer 1

Large, complex molecules composed of long chains of monomers joined together

Question 2

What are monomers?

Answer 2

Basic molecular units, e.g. monosaccharides, amino acids, nucleotides

Question 3

What monosaccharides make up carbohydrates?

Answer 3

Glucose, Fructose, Galactose

Question 4

How many carbon atoms are in each molecule of glucose?

Answer 4

6

Question 5

What is the structural difference between alpha glucose and beta glucose?

Answer 5

The H and OH groups on the right of the molecules are reversed

Question 6

What reaction joins monosaccharides together?

Answer 6

Condensation reaction. The molecules join together with the formation of a glycosidic bond, and a molecule of water is released.

Question 7

When two monosaccharides join, what is formed?

Answer 7

A disaccharide

Question 8

What are the 3 disaccharides you need to know, and what two molecules are they each made up of?

Answer 8

Maltose= glucose + glucose 
Sucrose= glucose + fructose 
Lactose= glucose + galactose

Question 9

What reaction breaks polymers apart and how does it break polymers apart?

Answer 9

Hydrolysis reaction. (basically the opposite of a condensation reaction) breaks polymers apart by the addition of a water molecule

Question 10

How to test for reducing sugars?

Answer 10

Benedicts Test.

• Add benedicts reagent (blue) to a sample and heat it in a water bath that has been brought to boil.
• If tests positive, a brick red precipitate will form.
• The higher the concentration of reducing sugar, the further the colour change goes (blue-green-yellow-orange-brick red)
• You can use ^ to compare amount of reducing sugar in diff solutions, a more accurate way of doing this is to filter solution & weigh precipitate.

Question 11

How to test for non-reducing sugars?

Answer 11

• Done if benedicts test is negative.
• First break sugar down into monosaccharides. Get new sample of test solution. Add dilute hydrochloric acid and carefully heat in a water bath thats been brought to the boil.
• The neutralise with sodium hydrogencarbonate
• Then carry out normal benedicts test
• If positive, coloured precipitate will form, if not it will stay blue(means it doesnt contain any sugar)

Question 12

What is a polysaccharide?

Answer 12

More than two monosaccharides (sugars) joined together by condensation reactions.

Question 13

What is starch used for in plants?

Answer 13

• Main energy storage (glucose) material in plants.

- Broken down to release glucose when energy is needed.

Question 14

Describe the two polysaccharides of alpha glucose that make up starch.

Answer 14

Amylose

• long chain
• angles of glycosidic bonds give it a coiled structure (compact- good for storage)

Amylopectin

• long chain
• branched. side branches allow enzymes that break down molecule to get at the glycosidic bonds easily, so glucose can be released quickly.

Question 15

What makes starch good for storage in plants?

Answer 15

• Its insoluble in water so doesnt affect water potential.

- Therefore, no water enters cells by osmosis (this would make them swell)

Question 16

How to test for Starch?

Answer 16

Iodine test.

• add iodine dissolved in potassium iodide solution to test sample.
• if starch is present, sample changes from browny orange to a blue black colour.

Question 17

What is the main energy storage material in animals?

Answer 17

Glycogen.

Question 18

Describe the structure of glycogen and why this aids its function in animals.

Answer 18

Very very branched.

• Loads of branches means that stored glucose can be released quickly, which is important for energy release (which needs to be quicker) in animals.
• Also makes molecule very compact (good for storage).

Question 19

What is the major component of cell walls in plants?

Answer 19

Cellulose

Question 20

Describe the structure of cellulose, and how this aids its function.

Answer 20

• Beta glucose molecules bonded to form straight cellulose chains.
• Chains are linked together (crosslinked over each other) by hydrogen bonds to form microfibrils (strong fibres).
• This means cellulose provides structural support for cells (plant cell walls).